The Epstein-Barr virus determined nuclear antigen (EBNA) is the only viral product regularly present in all EBV-transformed cells. We have purified it to homogeneity and found it to be composed of a 48K subcomponent. EBNA also appears to associate with a cellular DNA binding protein with a subunit size of 53K. The purpose of the present project is to analyze EBNA, 53K, and the complex biochemically, functionally and with regard to immunological specificity. We shall also compare EBNA with other nuclear antigens that we have detected in other lymphotropic virus transformed human and simian cell systems. In addition to EBNA itself, we shall also analyze a number of early, DNA binding, EBV-determined nuclear antigens that appear immediately upon the induction of the viral cycle by butyrate and other chemicals. In addition to the characterization of these components, we shall also investigate their possible relationship to EBNA.